AM6442: Reserved CMA memory allocation

Hello Brian,

Please post the changes you made to your memory configuration.

For example, on AM64x EVM, I see Linux devicetree under arch/arm64/boot/dts/ti/k3-am642-evm.dts and uboot devicetree under arch/arm/dts/k3-am642-evm.dts both list 2GB of RAM:

        memory@80000000 {
                device_type = "memory";
                /* 2G RAM */
                reg = <0x00000000 0x80000000 0x00000000 0x80000000>;

        };

Did you change that in your design?

Regards,

Nick

Hello Nick,

Many thank you for your response soon,

This issue is one of the problems you have ever supported me (IPC shared memory adjustment worked well on this but CMA has issue)

Because my custom board: LPDDR4 512MB so I need to change the memory layout for u-boot and kernel as below:

	memory@80000000 {
		device_type = "memory";
		/* 512MB RAM */
		reg = <0x00000000 0x80000000 0x00000000 0x20000000>;
	};
	reserved-memory {
		#address-cells = <2>;
		#size-cells = <2>;
		ranges;

		secure_ddr: optee@9e800000 {
			reg = <0x00 0x9e800000 0x00 0x01800000>; /* for OP-TEE */
			alignment = <0x1000>;
			no-map;
		};

		mcu_m4fss_dma_memory_region: m4f-dma-memory@91000000 {
			compatible = "shared-dma-pool";
			reg = <0x00 0x91000000 0x00 0x100000>;
			no-map;
		};

		mcu_m4fss_memory_region: m4f-memory@91100000 {
			compatible = "shared-dma-pool";
			reg = <0x00 0x91100000 0x00 0xf00000>;
			no-map;
		};

		rtos_ipc_memory_region: ipc-memories@95000000 {
			reg = <0x00 0x95000000 0x00 0x00800000>;
			alignment = <0x1000>;
			no-map;
		};
	};

This is error log:

[    0.000000] Initmem setup node 0 [mem 0x0000000080000000-0x000000009fffffff]
[    0.000000] cma: Failed to reserve 512 MiB

How to adjust the CMA memory size to 64MiB?

Thanks,

Brian

Hello Brian,

I am going to give you a response that I have not had time to test myself. Please let me know if it does not work, or if there is additional information future readers should know before going through these steps.

One of my team members indicated that the CMA buffer size is calculated based on the kernel page size. If that is true, you should see a smaller CMA allocation by selecting a smaller kernel page size. I have not looked into whether there are other ramifications of changing the kernel page size.

When I check on the AM64x EVM, it looks like the page size is 64kB by default:

root@am64xx-evm:~# getconf PAGESIZE
65536

You can use adjust the kernel configuration by following the steps at https://software-dl.ti.com/processor-sdk-linux/esd/AM64X/08_01_00_39/exports/docs/linux/Foundational_Components_Kernel_Users_Guide.html

Use menuconfig to adjust the kernel configuration. Go Kernel Features-->Page size(64KB). Select 4KB, then save the new kernel configuration. Then rebuild the kernel following the steps in the kernel users guide.

Let me know what you end up seeing.

Regards,

Nick

Hello Nick,

CMA can register with 24MiB, or 64MiB on AM64xx.

Thank you so much.

Brian

Hello Brian,

Circling back: do you need any additional guidance here?

Regards,

Nick